# git rev-parse -q --verify f9bc9bbe8afdf83412728f0b464979a72a3b9ec2^{commit} f9bc9bbe8afdf83412728f0b464979a72a3b9ec2 already have revision, skipping fetch # git checkout -q -f -B kisskb f9bc9bbe8afdf83412728f0b464979a72a3b9ec2 # git clean -qxdf # < git log -1 # commit f9bc9bbe8afdf83412728f0b464979a72a3b9ec2 # Author: Nicholas Piggin # Date: Mon Oct 16 22:43:00 2023 +1000 # # powerpc/qspinlock: Fix stale propagated yield_cpu # # yield_cpu is a sample of a preempted lock holder that gets propagated # back through the queue. Queued waiters use this to yield to the # preempted lock holder without continually sampling the lock word (which # would defeat the purpose of MCS queueing by bouncing the cache line). # # The problem is that yield_cpu can become stale. It can take some time to # be passed down the chain, and if any queued waiter gets preempted then # it will cease to propagate the yield_cpu to later waiters. # # This can result in yielding to a CPU that no longer holds the lock, # which is bad, but particularly if it is currently in H_CEDE (idle), # then it appears to be preempted and some hypervisors (PowerVM) can # cause very long H_CONFER latencies waiting for H_CEDE wakeup. This # results in latency spikes and hard lockups on oversubscribed # partitions with lock contention. # # This is a minimal fix. Before yielding to yield_cpu, sample the lock # word to confirm yield_cpu is still the owner, and bail out of it is not. # # Thanks to a bunch of people who reported this and tracked down the # exact problem using tracepoints and dispatch trace logs. # # Fixes: 28db61e207ea ("powerpc/qspinlock: allow propagation of yield CPU down the queue") # Cc: stable@vger.kernel.org # v6.2+ # Reported-by: Srikar Dronamraju # Reported-by: Laurent Dufour # Reported-by: Shrikanth Hegde # Debugged-by: "Nysal Jan K.A" # Signed-off-by: Nicholas Piggin # Tested-by: Shrikanth Hegde # Signed-off-by: Michael Ellerman # Link: https://msgid.link/20231016124305.139923-2-npiggin@gmail.com # < /opt/cross/kisskb/korg/gcc-13.1.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version # < /opt/cross/kisskb/korg/gcc-13.1.0-nolibc/powerpc64-linux/bin/powerpc64-linux-ld --version # < git log --format=%s --max-count=1 f9bc9bbe8afdf83412728f0b464979a72a3b9ec2 # make -s -j 32 ARCH=powerpc O=/kisskb/build/powerpc-fixes_mpc85xx_defconfig+KVM_powerpc-gcc13 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-13.1.0-nolibc/powerpc64-linux/bin/powerpc64-linux- mpc85xx_defconfig Using /kisskb/src/arch/powerpc/configs/mpc85xx_base.config as base Merging /kisskb/src/arch/powerpc/configs/85xx-32bit.config Merging /kisskb/src/arch/powerpc/configs/85xx-hw.config Merging /kisskb/src/arch/powerpc/configs/fsl-emb-nonhw.config # # merged configuration written to .config (needs make) # # Added to kconfig CONFIG_PPC_E500MC=y # Added to kconfig CONFIG_VIRTUALIZATION=y # Added to kconfig CONFIG_KVM_E500MC=y # Added to kconfig # < make -s -j 32 ARCH=powerpc O=/kisskb/build/powerpc-fixes_mpc85xx_defconfig+KVM_powerpc-gcc13 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-13.1.0-nolibc/powerpc64-linux/bin/powerpc64-linux- help # make -s -j 32 ARCH=powerpc O=/kisskb/build/powerpc-fixes_mpc85xx_defconfig+KVM_powerpc-gcc13 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-13.1.0-nolibc/powerpc64-linux/bin/powerpc64-linux- olddefconfig .config:4541:warning: override: reassigning to symbol PPC_E500MC .config:4542:warning: override: reassigning to symbol VIRTUALIZATION # make -s -j 32 ARCH=powerpc O=/kisskb/build/powerpc-fixes_mpc85xx_defconfig+KVM_powerpc-gcc13 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-13.1.0-nolibc/powerpc64-linux/bin/powerpc64-linux- In file included from /kisskb/src/include/linux/build_bug.h:5, from /kisskb/src/include/linux/container_of.h:5, from /kisskb/src/include/linux/list.h:5, from /kisskb/src/include/linux/module.h:12, from /kisskb/src/drivers/net/ethernet/freescale/fs_enet/mac-scc.c:15: /kisskb/src/drivers/net/ethernet/freescale/fs_enet/mac-scc.c: In function 'allocate_bd': /kisskb/src/include/linux/err.h:28:49: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast] 28 | #define IS_ERR_VALUE(x) unlikely((unsigned long)(void *)(x) >= (unsigned long)-MAX_ERRNO) | ^ /kisskb/src/include/linux/compiler.h:77:45: note: in definition of macro 'unlikely' 77 | # define unlikely(x) __builtin_expect(!!(x), 0) | ^ /kisskb/src/drivers/net/ethernet/freescale/fs_enet/mac-scc.c:138:13: note: in expansion of macro 'IS_ERR_VALUE' 138 | if (IS_ERR_VALUE(fep->ring_mem_addr)) | ^~~~~~~~~~~~ Completed OK # rm -rf /kisskb/build/powerpc-fixes_mpc85xx_defconfig+KVM_powerpc-gcc13 # Build took: 0:02:16.137699